1. Field of the Invention
The present invention relates to a circuit design, and more particularly, to a circuit design of a pulse width modulation (PWM) controller and the application thereof.
2. Description of the Related Art
A PWM controller is widely used in a switching voltage regulator. FIG. 1 shows a hint diagram of a prior PWM controller that controls a switch voltage regulator 10. The PWM controller 18 provides a plurality of switch control signals to control the on/off states of a high side switch 12 and a low side switch 14. By the control of the on/off states, an input voltage Vin can be transformed into a stable output voltage Vout.
FIG. 1 shows a prior switch voltage regulator 10, which includes a high side transistor 12 and a low side transistor 14 connected in series between an input voltage Vin and a ground potential GND. The switch control signal includes a UGATE signal for controlling the on/off state of the high side transistor 12, an LGATE signal for controlling the on/off state of the low side transistor 14. The common node 110 of the high and low side transistors is coupled to an output stage 112, which includes a low-pass filter composed of a capacitor C and inductor L and a load circuit RL, where the load circuit RL is driven by the output voltage Vout of the switch voltage regulator 10.
Generally, the PWM controller 18 features multiple functions if implemented in a single chip, such as over-current protection, under voltage lockout (UVLO), and enable/disable control. The over-current protection is used to detect the current flowing through the high side transistor 12 or low side transistor 14. If the current is larger than an over-current threshold, the PWM controller is stopped so as to protect the components of the switch voltage regulator from being damaged by a large current. The UVLO function is to temporarily lock the PWM controller 18 if the input voltage Vin is lower than a threshold. The consideration of the UVLO function is to reduce static power consumption and increase the reliability of the output voltage Vout. The function of the enable/disable signal is to activate and deactivate the operation of the PWM controller. In addition, a power-sensing function can be used to detect the input voltage Vin of the switching voltage regulator. If the input voltage Vin is greater than a threshold, the PWM controller is prepared for activation so as to shorten the time to boot the switching voltage regulator.
However, it is a general requirement to implement a powerful chip but at the same time limit the number of pins in a package. Therefore, to implement the above functions without increasing the number of pins is a major objective of PWM controller chip design.